1. Field of the Invention
The present invention relates to a system and method for controlling electromagnetically operated intake and exhaust valves of an internal combustion engine.
2. Prior Arts
An elctromagnetically operated valve mechanism is of a valve driving technique in which a valve body is operated by generating magnetic force in an actuator by supplying current thereto and there are numerous proposed techniques relating to that mechanism. The electromagnetically operated valve mechanism is characterized in that the construction of the valve driving mechanism can be simplified because of the absence of a cam mechanism and further the valve opening and closure timing of the intake and exhaust valves can be selectively established according to engine operating conditions, this enabling a wide range of selection of engine output characteristics and further leading to an improvement of fuel economy.
FIG. 14 is a schematic cross sectional view showing an example of an electromagnetically operated valve mechanism according to the prior art. The shown electromagnetically operated valve mechanism is an example employed on the exhaust valve side. With respect to the intake valve side, its detailed description will be omitted because of a similar construction. As shown, generally, the electromagnetically operated valve mechanism 110 comprises a valve body 120, an electromagnetic force generating section 130, a biasing section 140 and an armature 150. Also the valve body 120 comprises a valve 121 and a valve stem 122 and it is reciprocatably supported by a stem guide 161 provided in a cylinder head 160.
The valve 121 is formed so as to have a close contact with a valve seat 164 provided around an exhaust port end 163. Further, the valve stem 122 is connected at the top end thereof with the armature 150 fabricated of magnetic material.
The electromagnetic force generating section 130 is constituted by an electromagnetic solenoid 131 for closing a valve (hereinafter, referred to as valve closing solenoid, an electromagnetic solenoid 132 for opening a valve (hereinafter, referred to as valve opening solenoid), a first core 133 for the valve closing solenoid 131 and a second core 134 for the valve opening solenoid 132. The armature 150 is inserted between the first and second cores 133, 134 so as to move vertically therebetween.
The biasing section 140 comprises a spring 141 for opening a valve (hereinafter, referred to as valve opening spring) and a spring 142 for closing a valve (hereinafter, referred to as valve closing spring). The valve opening spring 141 is provided between the first core 133 and the valve stem 122 so as to bias the valve body 120 in the opening direction (downward direction in this drawing) with a specified biasing force. Further, the valve closing spring 142 is provided between the second core 134 and the armature 150 so as to bias the valve body 120 in the closing direction (upward direction in this drawing) with a specified biasing force.
When the valve closing solenoid 131 and the valve opening solenoid 132 are both deenergized, the valve opening spring 141 and the valve closing spring 142 have such a biasing force respectively that the armature 150 is sustained at about the mid-point between the first and second cores 133, 134. Therefore, when either of these solenoids 131, 132 is energized, the armature 150 can be attracted with less attraction force.
Describing an operation of this valve mechanism briefly, first, when the valve closing solenoid 131 is energized, an electromagnetic force is generated in the valve closing solenoid 131 to attract the armature 150 in the direction of the valve closing solenoid 131 against the biasing force of the valve opening spring 141 and as a result the valve body 120 travels in the closing direction (upward direction in this drawing) until the valve 121 comes into close contact with the valve seat 164. Thus, the combustion chamber 165 is sealed up against the exhaust port 162.
When the valve opening solenoid 132 is energized, the armature 150 is attracted toward the valve opening solenoid 132 to move the valve body 120 in the opening direction (downward direction) until the valve 121 is fully open.
FIG. 14 shows a state in which the electromagnetic force generating section 130 is deenergized and the armature 150 is positioned at the mid-point of the first core 133 and the second core 134.
Japanese Patent Application Laid-open No. Toku-Kai-Shou 61-76713 discloses an electromagnetically operated valve control system in which the valve speed immediately before seating on the valve seat is reduced to alleviate an impact when seated. Further, Japanese Patent Application Laid-open No. Toku-Kai-Hei 7-224624 discloses an electromagnetically operated valve train apparatus wherein the lift amount is detected by a lift sensor.
In applying the foregoing electromagnetically operated valve train system to a multi-cylinders engine, the current control must be performed per respective electromagnetic solenoids provided on each cylinder. In case of an electromagnetically operated valve train system as shown in FIG. 14, two electromagnetic solenoids, one for opening the valve and the other for closing the valve, are employed. Therefore, for example, in case of a four cylinders-four valves engine, thirty-two (32) electromagnetic solenoids must be controlled independently.
In order to generate signals for driving these numerous electromagnetic solenoids in the micro-computer in a timely manner, it is necessary to increase the number of channels and to enlarge the computing capacity of the micro-computer. Further, when performing such a fine valve opening and closing control as proposed in Toku-Kai-Shou 61-76713 or Toku-Kai-Hei 7-224624, still greater burden is charged on the micro-computer.
Therefore, in order to perform the above-mentioned valve opening and closing control, a high performance computer must be used, this resulting in a cost increase of the system.